Developed toner images in electrostatographic processes can be transferred and fused to another substrate such as paper. Transfer of the toner image can be accomplished by electrostatic methods, pressure contact, or other means. Once transferred, the toner image can be fused or fixed to the paper. The fusing step commonly consists of passing the paper on which toner powder is distributed in an imagewise pattern, through the nip of a pair of rolls, at least one of which is heated. The heated roller is often referred to as a fusing roller.
Toner fusing rollers have a cylindrical core which may contain a heat source in its interior, and a resilient covering layer formed directly or indirectly on the surface of the core. Roller coverings are commonly fluorocarbon polymers or silicone polymers, such as poly(dimethylsiloxane) polymers, of low surface energy which minimizes adherence of toner to the roller.
One persistent problem in this operation is that when the toner is heated during contact with the fusing roller, it may adhere not only to the paper but also to the fusing member. Any toner remaining adhered to the member can cause a false offset image to appear on the next sheet and can also degrade the fusing roller. Any toner or dirt stuck to the roller should be easily removable.
In the past, fusing rollers often had to be cleaned several times before their useful life ran out. This meant that printing time was wasted while somebody physically opened the machine and wiped down the fusing roller. In the case of the high-speed reel paper printers like the one we have described below, the fusing rollers had to be cleaned once every 25,000 copies. This meant that every 2 days or so, the printers had to be opened and the fusing rollers cleaned.
Frequently release oils composed of, for example, poly(dimethylsiloxanes), are also applied to the roller surface to prevent adherence of toner to the roller. Such release oils may interact with the roller surface upon repeated use and in time cause swelling, softening and degradation of the roller. Silicone rubber covering layers which are insufficiently resistant to release oils and cleaning solvents are also susceptible to delamination of the roller cover after repeated heating and cooling cycles. For the high speed printers, every 2 weeks or so the fusing roller needed to be replaced. This also cost more time and money.